Dog Urine Has Acute Impacts
Urban residents and their pets utilize urban greenspaces daily. As urban dog ownership rates increase globally, urban greenspaces are under mounting pressure even as the benefits and services they provide become more important. The urine of dogs is high in nitrogen (N) and may represent a significant portion of the annual urban N load. We examined the spatial distribution and impact of N deposition from dog urine on soils in three urban greenspace typologies in Finland: Parks, Tree Alleys, and Remnant Forests. We analyzed soil from around trees, lampposts and lawn areas near walking paths, and compared these to soils from lawn areas 8 m away from pathways. Soil nitrate, ammonium, total N concentrations, and electrical conductivity were significantly higher and soil pH significantly lower near path-side trees and poles relative to the 8 m lawn plots. Also, stable isotope analysis indicates that the primary source of path-side N are distinct from those of the 8 m lawn plots, supporting our hypothesis that dogs are a significant source of N in urban greenspaces, but that this deposition occurs in a restricted zone associated with walking paths. Additionally, we found that Remnant Forests were the least impacted of the three typologies analyzed. We recommend that landscape planners acknowledge this impact, and design parks to reduce or isolate this source of N from the wider environment.
We collected soil samples from 22 August to 13 September 2018. Next to a main pathway at each site, we collected composite samples of eight sub-samples from the top 10 cm of soil using a stainless steel push corer (3 cm ø) at: (1) a deciduous tree (Acer, Tilia, Ulmus, Betula or Quercus sp.), (2) a utility or lamppost, and (3) a lawn area. Lawn areas were selected to be >5 m away from any objects (e.g., benches, trash bins, lampposts), and outside of the tree canopy where possible. At trees and poles, one composite sample was taken from within 30 cm around the item and a second one from within an area of 1 m2 centered at 1 m from the edge of the item opposite the pathway. From the lawn, one composite sample was taken from within a 0.5 m2 area immediately adjacent to the path, and the second from within 1 m2 centered at 1 m from the path edge.
We have shown that dog-deposition is localized and impacts soil chemistry in urban greenspaces significantly. Supporting the first hypothesis, soil chemical characteristics and δ15N values around path-side trees and poles were significantly different from those located further from the paths and from lawn area soils next to the same pathway. Differences we observed in the δ15N values of soil samples taken from path-side trees and poles at 0 m and 8 m away suggest that the primary N inputs to these areas are derived from different sources. However, contrary to expectations, we found no difference in the measured variables between the path-side (0 m), 1 and 8 m lawn samples, indicating that path-side trees and poles act as focal points for dog-deposition, while lawn areas do not. This is likely a function of gender-specific differences in dogs’ urinating and scent-marking behaviors (countermarking), with male dogs preferring to urinate directly on trees and poles (overmarking) while females generally do not, instead preferring to urinate near, but not at the same locations as other dogs
Acknowledgments
We thank Marianne Lehtonen and Jukka Pellinen of the University of Helsinki’s Environmental Laboratory for their material support and help in analyzing our samples, and Changyi Lu for his help in the field. We are also grateful to Juha Raisio from the City of Helsinki Environmental Office, and Markku Saari from the Lahti City Parks Department for granting us permission to work in the cities’ parks.
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